Snap-open blister type containers have become an increasingly popular solution to a variety of packaging problems. Such containers are an excellent means for distributing samples of medicines, foodstuffs, or cosmetics as they are extremely lightweight, cheaply mailable, extremely inexpensive to manufacture, and yet are effective in securing and dispensing their contents. Such containers also provide a good means for stores to display and advertise the substance contained within. The broad, flat bubble forming the blister compartment of the container is easily air plug assist fabricated from a transparent plus coloured plastic sheet material well suited to display the contents of the container, while the broad, flat flange element typically formed around the blister compartment is readily secured to a cardboard display card easily hung on a display rack.
However, snap-open blister containers have, up to now, been limited to single use or throw-away containers, since they suffer from one distinct disadvantage--that of securely re-sealing the lid once it has been opened. One of the least expensive and most effective of the prior art solutions to this problem is the invention set forth in the disclosure of the Siegal U.S. Pat. No. 3,913,734. Here, the reclosability problem is solved by forming the backing member of the blister container from a sheet material having a mechanical "memory", and providing the portion of the flange surrounding the nozzle with a transverse weakened segment which is aligned with the frangible segment of the nozzle. Thus, when the transverse weakened segment of the flange folded back to break the frangible segment of the nozzle to form a nozzle opening, a hinge type structure is formed along the fold which seeks to re-align itself back into the substantially flat orientation it "remembers", thereby sealingly rejoining the nozzle lid back over the nozzle opening. Another embodiment of the invention disclosed in the Siegal patent comprises all the features of the previously described closure assembly, with the addition of providing the flange in the vicinity of the transverse weakened section with an arcuate cross section. The arcuate shape of this cross section cooperates with the flexible backing sheet sealingly engaged to the flange to provide an over center force tending to "pop" the lid over the nozzle opening when the hinge dividing the flange is close to resuming the flat, 180.degree. alignment it "remembers".
The weakness of the Siegal invention is the fact that once the blister container disclosed therein is opened, any relatively small shear force applied across the "hinge" will break the seal and reopen the container, which could result in spillage or leakage of the contents. Accordingly, there exists a need for a snap-open blister container with a lid which is not only re-sealable, but also readily securable once it is closed over the nozzle opening.